1. Field of the Invention
Embodiments of the invention relate to a hard disk drive. More particularly, embodiments of the invention relate to a hard disk drive that maintains a write property at a constant level even when the hard disk drive is used under a condition different from one intended by the manufacturer and an associated method for optimizing write parameters of a hard disk drive.
2. Discussion of Related Art
Hard disk drives (HDDs) are memory devices that record and reproduce data by converting digital electric pulses into a magnetic field. HDDs are widely used as auxiliary memory devices for computer systems to accommodate fast access time to a large amount of data. A HDD writes and reads data using a magnetic head. Typically, the magnetic head includes a write head for writing data and a read head for reading data. When the write head is located at a target track of the disk to form a magnetic field, the target track is magnetized so that data is written to a corresponding track. The read head reads the data by detecting the magnetic field of the track where the data is written. The data can be smoothly recorded when the write head magnetizes the target track with a magnetic field having an appropriate strength. However, when the strength of the magnetic field formed by the write head is too small (i.e. weak write), data recording at the target track fails. When the strength of a magnetic field formed by the write head is too large (referred to as adjacent track erasure (ATE)), data that is already recorded on other tracks adjacent to the target track is erased.
The strength of the magnetic field formed by the write head is determined by the current supplied to the write head. FIG. 1 shows a typical waveform of such a current. As time passes, the current supplied to the write head characteristically increases to the maximum, drops to a certain value and maintains a constant value. The current maintained at the constant value as time passes is referred to as a write current (WC). Also, current in excess of the WC just before the WC is supplied to the write head is referred to as an “overshoot”. The time for maintaining the overshoot is referred to as the “overshoot duration” (OSD). The difference between the maximum of the overshoot and the WC is referred to as “overshoot amplitude” (OSA).
The WC, OSD, and OSA parameters determine the strength of a magnetic field of the write head. A method for finding the most appropriate values of these parameters in the manufacturing process of a hard disk drive is described below. For example, in a method for finding the optical WC, the Nth track on a disk is selected to record data. After recording the data, a bit error rate (BER) is measured. Then, data is recorded at adjacent tracks, ((N+1)th and (N−1)th tracks) a predetermined number of times and the BER of the Nth track is measured. These steps are repeated by changing the WC value. When the difference in the BER before and after the measurement is not greater than a predetermined criteria or value, the optimal WC is set.
The write characteristic of the write head also varies according to the temperature condition of the hard disk drive. That is, when the temperature of the hard disk drive is different even if other parameters (e.g. WC, OSD, and OSA) are the same, the write characteristic of the write head can be changed. When write parameters are selected in a method which does not consider the temperature condition of the hard disk drive and the temperature condition of the hard disk drive is changed, the selected write parameters are difficult to maintain at a level to accommodate the characteristics associated with the write head.